Teardown: LED light shrinks size, cost with non-isolated driver

LED bulb prices are dropping. A year ago you could expect to pay $50 for a Philips dimmable 60W-replacement LED bulb, while today you can go to Best Buy and purchase its house brand 8W, 800 lumens Insignia 60W-replacement bulbfor just $17. What has changed in LED bulb design to allow this price drop? Tearing apart the bulb gives us a look into some design trends in LED lighting, such as how the LEDs are placed within the bulb and what driver architecture is used.

The Insignia bulb has a shape similar to the familiar incandescent light, with the addition of three metal heat sink fins, and a plastic bulb instead of glass (Figure 1).

Figure 1

Dimming is an important bulb characteristic for the US market. I used a Lutron Maestro dimming switch, with a programmable dimming control, and did a side-by-side comparison with an incandescent bulb. The Insignia dimmed consistently and smoothly, with a dimming profile similar to the incandescent bulb. You can watch a video of the dimming test here.

The next step was to look inside the bulb and see how the LEDs are mounted. Figure 2 shows the plastic bulb cover removed with a Dremmel tool, exposing the six Cree white LEDs that illuminate the bulb's light mixing chamber that allow an even glow with no pixelation. The metal fins that the LEDs are mounted on serve to both elevate the LEDs and serve as heat sinks.

Figure 2

At the bottom of the mixing chamber is a paper-thin aluminum reflector that helps reflect the light up and out of the bulb.

All of the electronics for this bulb lie beneath the mirror in the base of the bulb, in a separate and encapsulated compartment (More detailed photos are here).

Removing the rubbery potting compound shows that the electronics are mounted on two separate pc boards that nestle together. Figure 3 shows the two pc boards separated and next to the bulb's base.

Why are we stuck on screw-in replacements for Edison lamps?
Yes, there are billions of Edison sockets out there that can be filled - but the future isn't written in stone. Dump the Edison screw-in replacements and think of something that works best for PN junction light emitters - what is that? I don't know but the prize goes to whoever thinks of the best solution to the new problem, not the old one.

And you're surprised? I worked in that industry awhile, windmills are generally sited where there's a high probability of high sustained winds ie up on hills and at or near the end of long 480V 3PH feeders. To translate that's kind of like putting up a lightning antenna network! You quickly realize these little "surge protector diodes" don't help you A BIT, your protection devices need to actually dissipate significant amounts of power (gas tube protectors help a little). Ever try "recovering" a backplane that's suffered a near-direct strike? Keeping these things up SOUNDS easy until you actually have to do it, then you start to appreciate that it's MUCH harder than it looks!

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Perhaps LED bulb costs could come down with separate low voltage lighting circuits. A step down transformer at each room would distribute low voltage for LED lighting instead of dealing with 120VAC at each bulb.

A few comments ...
1) Not to be too picky, but I think it is 9 LED chips and not 6 ...
2) A large part of the power supply complexity and parts count (and much of the need for those pesky electrolytic caps) arises out of the need or desire to control power factor. To achieve an Energy Star rating the power factor must be good. This is not a requirement for UL listing as far as I know. Good power factor helps the electric company but is actually detrimental to the customer(at least in the short term) because electric meters do not measure or charge for the 'imaginary' component of power present in poor power factor equipment.
3) I do see the need, at least for the present retrofit market, to make lighting products that are backward compatible with existing fixtures, but the real future and advantage of LED lighting will be achieved with fixture and architectural designs that take maximum advantage of the desirable features of the LED source. See for example the LED 'strip lights' which are becoming widely available at reasonable cost. These are a distributed light source which is more desirable in many architectural designs, and by distributing the LEDS instead of concentrating them the heat dissipation problems go away. In my personal architectural applications I am using DC powered LEDs, which permit direct use of low voltage power source derived from solar without the inherent loss of efficiency arising from converting stored DC to AC and then back to regulated DC at the fixture. The parts count for the LED current regulator is 1 IC and no capacitors are used. But this approach requires a fully integrated design from power source through power distribution (at 12-36VDC) to LED fixture. DC designs can of course also be powered by UL listed class 2 'wall warts' allowing the choice of AC or DC power source, and providing an inexpensive and easily replaceable alternative for the short lived AC power supply.

These little (sometimes large) caps are the bane of most power electronics; will need some alternative or a lot development for renewable energy to really kick in. As an example windmills typically have a 25 year 'warranty', but the power electronics is covered under a 'maintenance' agreement.

Myth of 50-year LEDS has to be nixed. Specially if additional electronics in the power circuit (such as motion-sensitive switching) spikes will shorten life of 'bulb' electronics. My CFLs last 'forever', but those with motion-sensor switching.